try. Yet, with the possible exception of the commercially available Encarsia forrnosa Gahan, their ability to suppress B. tabaci populations under a variety of conditions has not been de- termined. Here we report our findings on pusillus (LeConte), one of the several natural enemies we are evaluating for use in B. tabaci biologi- E cal control programs in field crops and greenhouse-grown poinsettias. I3 1: 1: 7 Small, shiny I Adult Delphastus pusillus feeding on a A third instar immature D. pusillus. Adult D. pusillus are small, shiny Bemisia tabaci nymph. black coccinellid 1.3 to 1.4 mm in length; the larvae are pale yellowish white. This beetle, related to aphid- feeding ladybird beetles, has been re- ported as a predator of various white- Predatory beetle may flies on citrus in Florida and Mexico and on cassava in Colombia, South up p ress iI ve rI eaf w hi tef Iy America. D. pusillus is distributed s s widely across the central and south- eastern United States, south through Kevin M. Heinz P James R. Brazzle o Charles H. Pickett Central America and into South Eric T. Natwick P Judy M. Nelson o Michael P. Parrella America as far as Peru. This geo- graphic range suggests that 6. pusillus should be able to survive and repro- The coccinellid beetle, Delphastus cotton and the development of sooty duce in the diverse California climate. pusillus, may be able to suppress molds. B. tabaci also drains nutrients D. pusillus is already found widely in the silverleaf (or strain B from the plant as it feeds. The drain on the coastal and subcoastal areas, sweetpotato) that has in- plant nutrients by enormous B. tabaci where it was introduced by Rose and fested California agriculture. Life populations feeding on crops from DeBach from 1966 to 1977 (California history characteristics of this spring through early fall has caused Agriculture, July-August 1981).Ac- predatoi indicate that it is most ef- much of the economic loss to south- cording to the results of laboratory fective as a biological control eastern California agriculture. In addi- studies conducted by University of agent at high whitefly densities. D. tion, over the past 4 years, B. tabaci has Florida scientists, the egg-to-adult- pusillus releases in Imperial Val- become the major whitefly species at- emergence development time for D. tacking California greenhouse crops. pusillus is 21 days at 28 3°C (82 ley cotton trials reduced immature 2 Explanations for the recent out- 5.4"F). By comparison, the develop- whitefly densities to one-third of breaks are speculative. However, one ment time for B. tabaci on cotton at a the densities found in cotton plots fact is certain: alternatives to current constant 27.5"C (82°F) is approxi- receiving no releases. whitefly management practices must mately 18 days. Larval and adult be developed if production is to be beetles feed on all stages of B. tabaci, Widespread infestation by the sustained in infested areas. Research- but the daily consumption of prey by silverleaf (or strain B sweetpotato) ers have begun examining the many adult beetles and the time required to whitefly, Bernisia tabaci (Gennadius), parasitoids and predators reported to consume prey are directly correlated has caused economic damage un- successfully establish on B. tabaci to the size or development stage of the matched in the history of agricultural throughout its geographic range. Be- whitefly. entomology to crops in the southwest- cause the distribution of B. tabaci en- Various biological parameters relat- ern United States and northern Mexico compasses a wide array of environ- ing to the efficacy of this predator (California Agriculture, September-Oc- mental conditions, host plants and (adult longevity, prey consumption tober 1992 and January-February agricultural practices, it is unlikely and fecundity as a function of whitefly 1993). B. tabaci serves as a vector for that a single species of parasitoid or density) were measured on two poin- plant pathogenic viruses, induces predator will control it. Fortunately, settia cultivars - 'Annette Hegg Bril- squash silverleaf in cucurbits and ir- many of B. tabaci's natural enemies en- liant Diamond' and 'Lilo'. Leaf hair, or regular ripening in tomatoes, and pro- demic to the United States are reared trichome, density, which is often nega- duces honeydew, which leads to sticky in laboratories throughout the coun- tively correlated with the searching ef-

CALIF'ORNIA AGRICULTURE, MARCH-APRIL 1994 35 ficiency of natural enemies, is one- were detected, but both lived signifi- over the same period, regardless of the third greater on ‘Lilo’ than on cantly longer than males feeding on poinsettia cultivar (F = 22.45, df = ‘Annette Hegg Brilliant Diamond’, e!%s. 1,155; p = 0.0001). Prey consumption hence the need to compare D. pusillus From these results, we conclude was also significantly greater on performance on the two cultivars. The that host plants that differ only in tri- ’Annette Hegg Brilliant Diamond’ (the interaction between D. pusillus and a chome density will probably not influ- cultivar with significantly fewer tri- parasitoid found in California and ence the adult longevity of D. pusillus. chomes) than on ‘Lilo’, whether the other areas, Encursiu pergundiellu Female and male adult beetles lived beetles fed on whitefly eggs or Howard, was measured on ‘Lilo‘ only. on average 64 and 36 days, respec- nymphs (F = 55.89, df = 1,155; p = During the studies, average daily tem- tively. These lifespans are 5 to 10 times 0.001). peratures were 27.0 f 1.5”C, (81 f 3°F) longer than adult longevities typically Results from these stud- and daily photoperiods were 16L:8D. reported for B. tubuci parasitoids. ies suggest that it may be easier for D. pusillus to locate whitefly nymphs than Adult longevity Prey consumption and egg laying eggs, and therefore beetles will reduce Adult D. pusillus longevity was We used the following procedure to whitefly nymph densities to a greater measured by placing a newly emerged study prey consumption and the num- extent than they will reduce egg densi- adult in a petri dish containing a poin- ber of eggs laid as functions of prey ties. Because a substantial amount of settia leaf infested with either B. tubuci density. Individual D. pusillus beetle natural mortality occurs during the eggs or third instar nymphs. The adults of unknown age were placed in first instar or crawler stage of B. tabaci dishes were checked daily for the pres- a small cage containing a three-leaf development, beetle predation on the ence of live adult beetles, and the poinsettia plant infested with third-in- later instars in the field should dra- leaves were changed every other day. star B. tubuci nymphs or eggs (the matically increase the overall level of Forty adults were evaluated per culti- number of which were determined by whitefly mortality and hence increase var, and poinsettia cultivar-dependent counting live and preyed-upon the overall potential for controlling differences in longevity were detected immatures at the end of the study). Af- . Furthermore, beetle preda- with a two-way analysis of variance ter a 3-day exposure period, the plants tion will be greater on host plants with and Tukey’s means separation test were removed and both the numbers fewer trichomes, again increasing the (fig. 1).Adult longevity did not vary of prey consumed and the number of chance of achieving successful control significantly between the two poinset- D. pusillus eggs oviposited were on these types of host plants. tia cultivars, but significant differences counted with the aid of a dissecting The number of eggs oviposited by between sex and prey item were de- microscope. Death of a whitefly due to females was significantly and posi- tected. Female adults feeding on B. D. pusillus predation can easily be dis- tively related to prey availability on tabaci nymphs lived significantly tinguished from death by other causes. ’Annette Hegg Brilliant Diamond’, but longer than males or females feeding Only a flattened, empty whitefly cu- no relationship existed between the on B. tubuci eggs. No significant differ- ticle is left after complete consump- number of ovipositions and prey den- ences between males feeding on tion, while in an incompletely con- sities on ’Lilo’ (fig. 3). Again, analysis nymphs and females feeding on eggs sumed whitefly, disrupted internal of covariance revealed differences be- organs are visible. This is compared to tween prey types and between culti- A ‘Brilliant Diamond’ death by dissication or leaf senescence, vars. Egg laying by female beetles did loO1 r T 0‘Lilo’ which are characterized by darkening 80 - B of the internal organs and gross defor- mation of the outer cuticle without 60- B A any puncture marks. 40 - The relationship between the den- C sity of available hosts and prey con- 20 - sumption was evaluated by least- squares linear regression. For both prey types and for both cultivars, a on on on on significant positive linear relationship nymphs nymphs eggs eggs existed between the number of prey Fig. 1. Mean longevity of D. pusillus consumed and the number of prey beetles preying on either B. tabacieggs or available (fig. 2). Analysis of covari- third instar nymphs f 1 SE. Vertical bars with the same letter are not statistically ance was used to detect differences be- different at p 0.05 (1-way ANOVA with tween prey types and between culti- Tukey’s means separation). Studies were vars. The number of whitefly nymphs conducted on two poinsettia cultivars; one consumed by individual beetles over a cultivar, ‘Annette Hegg Brilliant Diamond’, has 33% fewer trichomes per unit area 3-day period was significantly greater than the second cultivar, ‘Lilo’. than the number of eggs consumed

36 CALIFORNIA AGRICULTURE, VOLUME 48, NUMBER 2 not differ significantly with the con- tabaci nymphs. If D. pusillus randomly and, after a 24-hour exposure period, sumption of whitefly eggs or whitefly forages on parasitized and unpara- the number of nymphs consumed was nymphs as prey items. However, egg sitized nymphs, parasitized nymphs counted (fig. 4, white bar). We exam- laying was significantly greater on should be preyed upon to the same ex- ined 20 D. pusillus larvae, and com- ’Annette Hegg Brilliant Diamond’ tent as unparasitized nymphs, assum- pared the observed numbers of each than on ‘Lilo’, regardless of whether ing equal handling times and encoun- age and size class of nymphs eaten to the beetles were feeding on eggs or ter rates between parasitized and the expected numbers. nymphs (F = 12.15, df = 1,79; p = unparasitized nymphs. Therefore, in The interaction between adult D. 0.0008). Although a definitive explana- our experiments, the number of para- pusillus and developing E. pergandiella tion is not possible at thi! time, the sitized nymphs consumed by ran- was examined in B. tabaci nymphs greater trichome density on ’Lilo’ domly foraging D. pusillus should be parasitized 1,5,9 or 13 days before ex- leaves may adversely affect the D. equal to the proportion of parasitized posure to beetles. The physical struc- pusillus oviposition rate by reducing B. tabaci nymphs on a leaf multiplied ture of immature E. pergandiella the number of prey the beetles can by the total number of nymphs con- changes significantly with time. One- consume. sumed by D. pusillus (figs. 4 and 5, and 5-day-old E. pergandiella larvae ad- solid bars). here (together with their hosts) to the Interactions with parasitoids We placed individual fourth-instar cuticle of whitefly nymphs, while 9- Because the release of several natu- D. pusillus larvae, which are also pre- and 13-day-old pupae are retracted ral enemy species may be necessary to daceous on immature whiteflies, on from the cuticular wall of their hosts. suppress B. tabaci populations, and be- single leaves possessing parasitized Fifteen unparasitized fourth-instar cause we wish to reduce the probabil- nymphs containing E. pergandiella lar- whitefly nymphs and 15 nymphs con- ity of detrimental interspecific interac- vae (approximately 7 days after ovipo- taining developing parasitoids were tions, we examined the interactions sition) or pupae (approximately 14 removed from infested plants and se- between D. pusillus and other natu- days after oviposition). Prepupal cured to an uninfested 18-cm2 poinset- rally occurring or released natural en- stages of E. pergandiella were character- tia leaf section with minute drops of emies. To examine the magnitude of ized by translucent larvae pressed honey. The leaf sections that contained one of these interactions, we provided against the whitefly cuticle; the pupal whiteflies and only one age class of D. pusillus a choice test of ‘Lilo’ poin- stages were characterized by tan pu- developing parasitoids were fixed to settia leaves infested with various pae that were retracted from the walls the bottoms of petri dish covers with stages of unparasitized and parasit- of the whitefly cuticle. The leaves were melted wax. Adult beetles were singly ized (by Encarsia pergandiella ) B. placed within individual petri dishes, placed on leaves, the covers replaced

AnnetteHegg AnnetteHegg ‘Brilliant Diamond’ ‘Lilo’ ‘Brilliant Diamond’ ‘Liio’

Eggs 1,000 - P 100- IlOO E a a g 10- 0

Nymphs Nymphs :1,000 1,000

-=jlio 0 10

I I -1 I I I 10 100 1.000 10 100 1.000 10 100 1,000 10 100 1,000 Number of prey available Number of prey available

Fig. 2. Prey consumption by D. pusillus beetles foraging on Fig. 3. Number of eggs oviposited by female beetles foraging on three-leaf poinsettias for 3 days. Data are plotted on a logarith- three-leaf poinsettia plants over 3 days. Data are plotted on a mic scale, and statistically significant (at p = 0.05) least-squares logarithmic scale, and statistically significant (at p = 0.05) least- linear regression lines are plotted for each cultivar and prey squares linear regression lines are plotted for each cultivar and type. The equations descrlbing these lines are: prey type. The equations describing these lines are: For ‘Annette Hegg Brilliant Diamond’, y = 0.98~- 0.38, r2= 0.626 For ‘Annette Hegg Brilliant Diamond’, y = 1.07~- 2.37, r2= 0.579 (B. tabacieggs as prey) and y = 0.91~+ 0.06, r2= 0.287 (B. tabaci (B. tabaci eggs as prey) and y = 1.01 x - 1.93, r2 = 0.306 (B. tabaci nymphs as prey) nymphs as prey) For ‘Lilo’, y = 1.08~- 1.28, r2 = 0.373 (B. tabaci eggs as prey) and y 0.46~+ 0.64, r2= 0.181 (B. tabaci nymphs as prey)

CALIFORNIA AGRICULTURE, MARCH-APRIL 1994 37 and the dishes inverted. After a 24- p < 0.05; and GP(Pupae)= 16.497, df = 1, Laboratory studies like the ones re- hour exposure time, the numbers of p < 0.001;) (fig. 5). The intensity of the ported here help to identify the poten- intact and preyed-upon parasitized interaction between adult D. pusillus tial strengths and shortcomings of a and unparasitized nymphs were deter- and developing E. pergandiella de- natural enemy's ability to suppress a mined. A total of 24 beetles was as- pends on the wasp's development whitefly population. Two other evalu- sayed for each of the four parasitoid stage. The frequency of beetle preda- ations have also been conducted to age classes, and the observed numbers tion on 1- and 5-day-old E. pergandiella quantify the potential of D.pusillus as of nymphs fed upon were compared was not significantly different from a successful biological control agent to the expected numbers. the expected frequency (GP(day and for B. tabaci. The goal of the first evalu- The observed frequencies deviated GP(day5) were not significant at p = 0.05). ation - a greenhouse study examin- significantly from the expected, as de- By contrast, beetle predation on 9- and ing the relative ability of three natural termined by calculating G-statistics 13-day-old E. pergandiella was signifi- enemy species to suppress B. tabaci in- from a replicated goodness-of-fit test cantly less than expected by random festing poinsettias - was to eliminate for both beetle larvae and adults. The chance (GP(da 9) = 16.391, df = 1, poorly adapted species from consider- advantage of this analysis is that the p < 0.001; ancr Gp(day13) = 49.019, ation as potential biological control overall goodness-of-fit test can be par- df = 1, p < 0.001). Because the GH sta- agents. The goal of the second evalua- titioned into separate G-tests repre- tistics were not significant at p = 0.05, tion - a field study conducted in Im- senting individual degrees of freedom we conclude that the beetles behaved perial Valley cotton -was to quantify between groups (G, statistic) and in a consistent manner within each of the level of suppression provided by within groups (GH statistic) in a man- the four treatments. D. pusillus releases relative to experi- ner analogous to that practiced in Results from these experiments in- mental controls that were not receiv- analysis of variance. It was therefore dicate that D. pusillus larvae and ing natural enemy releases. possible to detect differences in preda- adults become more discriminating as tion by adult beetles among parasitoid the parasitoid develops. Larvae and Greenhouse poinsettia trial age groups. adult predation on parasitoid larvae Four large cages (4 ft wide by 6 ft Results from this test indicate that (27 days old) indicate that parasitoid long by 3 ft high) covered with cotton all beetle larvae behaved in a consis- populations may be adversely affected organdy were erected in a greenhouse tent manner (GH(Prepupae) and GH(l'upae) by D. pusillus. However, whether this on the UC Davis campus. Twenty-four statistics were not significant at p = potential negative impact on parasi- 1-month old 'Lilo' poinsettia plants 0.05), and that they tended to feed on toid populations reduces the chance of transplanted into 6-inch-diameter pots parasitized nymphs significantly less achieving successful biological control were placed in each cage. Interplant than would be expected by random cannot be determined until further spacing was 1 ft, a distance similar to chance (GP(Prepupae)= 5.591, df =1, data are collected. that used by commercial poinsettia growers. In the 3 weeks immediately Expected after the plants were positioned within the cages, 24 adult whiteflies were re- Observed leased into the cages each week to r: Q start a B. tabaci infestation. After the u) 1.0- - third whitefly release, weekly releases c a Expected 8- Is 0 Observed of natural enemies were initiated at a rate of 3 individuals per plant per EC E" - q 6- week. Releases continued over the 12- 0 0.5 - N 3 24- week duration of the study. One cage .- f: .-c .=.s m u) receiving no natural enemy releases @ 2- E acted as an experimental control, and ns 0.0 one each of the three remaining cages Larvae Pupae received releases of D. pusillus and the Parasitoid development stage parasitoids Encarsia luteola Howard Fig. 4. Interaction of D. pusi//us larvae with Fig. 5. Interaction of D. pusillus adults and Encarsia pergandiella. Each week, two development stages of E. with four development stages of E. one leaf was sampled at random from pergandiella. The expected values are the pergandiella. The expected values are the each plant within a cage, and the num- proportion of available parasitized proportion of available parasitized ber of live whiteflies was recorded by nymphs multiplied by the total number of nymphs multiplied by the total number of nymphs consumed (solid bars f 1 SE). nymphs consumed (solid bars k 1 SE). development stage for each leaf. Be- The white bars (-+1 SE) represent the ob- The white bars (-+1 SE) represent the ob- tween-treatment differences were de- served number of nymphs preyed upon by served number of nymphs preyed upon by tected using Wilcoxon's signed-ranks immature beetles. Asterisks indicate treat- adult beetles. Asterisks indicate treat- test for two groups, arranged as paired ments in which observed values are sig- ments in which observed values are sig- nificantly different from expected values nificantly different from expected values observations. In this test, the data are (p = 0.05). (p = 0.05). treated as randomized blocks, with

38 CALIFORNIA AGRICULTURE, VOLUME 48, NUMBER 2 sample dates as blocks and the species nate edge effects. A stratified random sities in fields not receiving the beetle differences as the fixed treatments to sample from the remaining 1/4 acre of releases. In the cages (fig. 71, signifi- be tested. each plot was collected weekly begin- cant between-treatment differences in Results of the trial are shown in fig- ning on July 14. Each plot was subdi- the whitefly densities were detected ure 6. Data for the no-release treat- vided into 30 subplots, and a vertically (F = 13.99, df = 1, p = 0.0096). Because ment are plotted for only the first 9 stratified leaf sample was collected the magnitude of this difference in- weeks of the study. Starting in week 9, from a plant randomly selected from creased dramatically between Septem- plants in the control cage began to each subplot. The vertically stratified ber 9 and October 14, a significant drop their lower leaves (which con- sample consisted of mainstem leaves sample DATE x TREATMENT effect was tained whitefly pupae) and die, prob- removed every 4 inches along the cen- also detected (F = 5.35, df = 13, ably because of severe khitefly infes- tral stem of each cotton plant. Four p = 0.0111). If sampling could have tations. Over these first 9 weeks, the plants from each of the eight cages been continued, it is possible that simi- whitefly densities in each cage receiv- were sampled in a similar fashion. The lar results would have been observed ing natural enemy releases were sig- number of live, dead and parasitized in the open fields. nificantly lower than the density ob- immature whiteflies was determined Parasitoids in the genera Encarsia served in the cage not receiving any for a 1.5-cm2 leaf punch taken from the and Eretmocersus, also found to be natural enemy releases. By week 9, re- center of each leaf sample. parasitizing whitefly nymphs, were leases of D. pusillus qualitatively pro- On July 4, plant stands in each plot not adversely affected by D. pusillus vided the best control by suppressing were counted and plots were paired releases. That is, parasitoid densities whitefly populations by almost 2 or- according to plant density. Within were not significantly reduced (F-sta- ders of magnitude relative to the con- each pair, one plot was designated for tistics calculated from repeated mea- trol. However, the average whitefly D. pusillus releases and the other plot density (over all sample dates) was not was designated a control plot. Cages significantly different from the aver- received the same designation (release 100,000 age whitefly density observed in the E. or no release) as the surrounding plot. s 10,000 luteola or E. pergandiella release cages. From July 21 through September 1 a The lack of statistical significance is (open fields) and September 17 E 1,000 probably due to the low number of (cages), four cotton plots and four -f -G No releases a replications within the trial. While the cages received weekly releases of D. t Encarsia p8rgandlella b 10 trial is currently being replicated, the pusillus. Equal numbers of beetles per -E looi + Delphastus pusillus t EncarsIaluteola results presented here should serve as plant were released each week; in to- 01 IIIII I1 11 IIII 0 1 2 3 4 5 6 7 8 9101112 hypotheses for further study. tal, 35,144 adult beetles were released Sample week into the four cages and open-field Imperial Valley cotton trial Fig. 6. Comparison of B. tabaci densities plots during the study. All beetle re- in poinsettia cages receiving releases of Eight %-acre plots of cotton (var. leases were carried out before 9 a.m. three different species of natural enemies. DPL5461) were planted at the UC The last of the open-field plot Sample weeks (weeks receiving natural enemy releases) are depicted along the x- Desert Research and Extension Center samples was taken on August 26 in or- axis. The y-axis represents the number of in El Centro, California, on May 5, der to remain in compliance with Im- immature whiteflies per plant (=the num- 1992. The plots were established in perial County regulations for boll ter- ber of whiteflies per leaf multiplied by the line with commercial practices, except mination no later than September 1. number of leaves per plant) on a logarith- mic scale. that no pesticides were applied during Because the cages were excluded from the crop cycle. The efficacy of D. these regulations, leaf samples were t D. pusiNus releases pusillus releases was to be examined collected from the cages through Octo- -0-Noreleases under conditions in which B. tabaci ber 14. and natural enemy movements were The effects of the D.pusillus releases present or absent. To prevent mass were evaluated by using a repeated movements of B. tabaci, whitefly exclu- measures analysis of variance to com- sion cages were constructed of sched- pare the whitefly densities in the re- ule 40 PVC pipe frames (6.67 ft wide lease areas with those in the non-re- by 10 ft long by 6 ft high) covered with lease areas. Data were transformed 42-mesh Lumite screening material. using a polynomial tranformation 14 July 28 July 12 Aug 26 Aug 9 Sept 23 Sept 7 Oct On July 14, one cage, covering ap- prior to analysis. No significant be- Sample week proximately 40 cotton plants, was arbi- tween-treatment differences could be Fig. 7. B. tabacidensities in cotton enclo- trarily placed into each of the eight detected in the open-field conditions. sure cages. The sample dates are depicted cotton plots. However, it is noteworthy that over along the x-axis, and the y-axis represents the number of immature whiteflies per cm2 A 27-feet-wide border of cotton the last three sample dates whitefly of leaf area. Whitefly densities are ex- plants was established around the densities in fields receiving D. pusillus pressed as the mean (N=4 replicates) f 1 outer perimeter of each plot to elimi- releases were declining relative to den- standard error (vertical bars).

CALIFORNIA AGRICULTURE, MARCH-APRIL 1994 39 Prey consumption was significantly greater on poinsettias that have fewer tri- sures analysis-of-varianc&n cotton evaluations of D. pusillus releases chomes, whether the beetles fed on white- plots receiving D. pusillus releases should be conducted to define with fly eggs or nymphs. compared to plots not receiving the re- greater precision the role of this preda- leases. These data suggest that D. tor within an overall management pro- Natwick is Imperial County Entomology pusillus can be released with no appar- gram for B. tabaci. A cooperative Farm Advisor, UC Cooperative Extension, ent adverse effects on existing parasi- project between UC Davis, the Biologi- Holtville, California. toid fauna, or that the beetles may be cal Control Program of the California The Delphastus pusillus were origi- used as one component of a multiple- Department of Food and Agriculture, nally supplied to UC Davis by the Univer- species release. and the UC Desert Research and Ex- sity of Florida and USDAIARS in Our results suggest that releases of tension Center has been initiated to Apopka, Florida. Kathleen Casanave, Bio- D. pusillus may suppress B. tabaci conduct such evaluations. logical Control Program, CDFA, reared populations. Introductions of this the D. pusillus for field release into the predatory beetle may provide a partial K. M. Heinz is Assistant Research Scien- Imperial Valley. Dr. Andrew Polaszek solution to the devastating B. tabaci tist, 1. R. Brazzle is a master's student, 1. from the Institute of Entomology, London, problem in Imperial County. D. M. Nelson is a doctoral student and M. P. performed parasitoid identification. Finan- pusillus may also be useful in manag- Parrella is Professor and Chair, all within cial support for this work was provided by ing patchy whitefly outbreaks in the Department of Entomology, Univer- the American Floral Endowment; the Cali- greenhouses containing ornamental sity of California, Davis; C. H. Pickett is fornia Association of Nurseymen; the crops that cannot tolerate even moder- Environmental Research Scientist with California Department of Food and Agri- ate whitefly densities. The study re- the Biological Control Program of the culture, Biological Control Unit; and UC- sults further indicate that additional, California Department of Food and Agri- IPM. Poinsettia plants were provided by large-scale greenhouse and field culture (CDFA),Sacramento, and E. T. Paul Ecke Poinsettias, Encinitas, California.

CALIFORNIA AGRICUL TUR€ ASSOCIATE EDITORS

Animal, Avian, Aquaculture Land, Air & Water Sciences and Veterinarv Sciences J. Brian Mudd Richard H. Mckapes Garrison Sposito (2nd assoc. editor to be announced) Henry J. Vaux, Jr. Economlcs and Public Policy Natural Resources Harold 0. Carter Daniel W. Anderson Alvin Sokolow John Helms Richard B. Standiford Food and Nutrition Barbara Schneeman Pest Management Eunice Williamson Michael Rust Frank Zalom Human and Community Development Linda M. Manton Plant Sciences Karen P. Varcoe Calvin 0. Qualsat G. Steven Sibbett 40 CALIFORNIA AGRICULTURE, VOLUME 48, NUMBER 2